The Redundancy of an Optimal Binary Fix-Free Code Is Not Greater Than 1 bit

Abstract

In the context of fix-free codes, the most important and immediate consequence of the 3/4-conjecture (if it is proven), is that the redundancy of an optimal binary fix-free code never exceeds 1 bit, as with the optimal prefix-free codes, i.e. Huffman codes. In this paper, this bound on the redundancy is proven without requiring the conjecture to be true. To do so, we use two known sufficient conditions for the existence of binary fix-free codes to derive an improved upper bound on the redundancy of an optimal fix-free code in terms of the largest symbol probability.